1. Field of the Invention
The present invention concerns a method to acquire a magnetic resonance image data set of a target volume with a magnetic resonance device.
2. Description of the Prior Art
Multi-slice acquisitions that can cover a large target volume by means of parallel slices are a known concept in magnetic resonance imaging. A direction is consequently designated along which a division of the target volume into multiple slices (slice selection direction) takes place one-dimensionally using a slice thickness. It is known to acquire the slices with temporal interleaving, meaning that the entire target volume is acquired as a slice package in the same measurement time in which one slice can be acquired at a predetermined contrast. The measurement time in which a single acquisition (single shot) of a slice is possible is typically designated as the repetition time, after which this same slice can be acquired again (in particular in multi-shot acquisitions). In other words, the temporally interleaved acquisition means that signals are acquired from N non-overlapping slices in the time interval of an Nth part of the repetition time. In comparison to a volume excitation with the same acquisition efficiency (excitations per time unit), the contrast-determining repetition time is extended by a factor of N. The saturation of the spin system by the repeated excitations is significantly reduced.
In addition, the acquisition of target volumes as a whole is known. For example, if the spinal column should be acquired as a target volume, using two radio-frequency pulses of a spin echo-based sequence one can select not only slices in one dimension but also parallelograms in two dimensions, by rotating the slice selection direction in the spin echo sequence of the excitation pulse counter to that of the refocusing pulse. The spin echo signal that is generated in such a manner originates from the intersection of the two rotated slices that are respectively selected with the excitation pulse and the refocusing pulse. In this way it is possible (for example in the case of the spinal column) to acquire the target volume as a complete subject, in contrast to multi-slice acquisitions in which the individual slices form only sub-volumes of the target volume.